This invention relates to the field of electronic circuit device testing and to radio frequency testing of surface acoustic wave die on a wafer.
Computer controlled automated probing of die on semiconductor wafers has been extensively used in the electronic circuit art for digital, analog, radio frequency, and discrete semiconductor components. The specialized technical problems and smaller degree of commercial activity associated with surface acoustic wave devices, including especially surface acoustic wave delay lines, has limited the feasiblility and the need for applying such probing to surface acoustic wave devices. A program has been sponsored by the United States Air Force to advance the art in manufacturing surface acoustic wave devices in order that reliable and low cost devices of this type be available for military signal processing needs; this program has initiated the extension of probing technology to the special needs of surface acoustic wave devices.
Surface acoustic wave delay lines are often fabricated on two or three inch probe accessible wafers that are made from such material as lithium niobate; usually each wafer contains forty or more delay lines with each delay line having two or more electric-to-acoustic and acoustic-to-electric transducers incorporated. Many such delay lines, for example, have a single input transducer and a plurality of output transducers located at intermediate delay points along the path traveled by the surface acoustic wave through the acoustic substrate. Frequently, each of the transducers will have a number of electrodes which are fabricated in the form of interleaved fingers.
The prevailing practice in the delay line manufacturing art is to visually inspect a wafer of delay line die in order that manufacturing defects such as improper etching, mask misalignment, and improper metallization be identified before the expense of further fabrication and packaging is incurred. Visual inspecting times of several minutes for each wafer are not uncommon--with the inspection results being greatly dependent upon the experience and fatigue level of the inspector.
The large volume manufacture of reliable surface acoustic wave devices clearly needs a replacement or supplement for this variable and expensive human oriented inspection practice. The computer-controlled automated probing used in the integrated circuit art appears to offer a ready solution to such human oriented inspection difficulties, however, the differences between a surface acoustic wave device and most integrated circuit devices has precluded an immediate adoption of integrated circuit probing techniques in the surface acoustic wave art.
The prior patent art includes numerous examples of computer-controlled and automated test equipment applied to analog and digital components and systems made from these components. In particular, U.S. Pat. No. 4,390,837 issued to Kevin Hotvedt is an example of automated testing involving digital and analog technology and the use of an oscilloscope display of test wave forms. Similarly, U.S. Pat. No. 4,196,386 issued to Donald E. Phelps concerns a test apparatus which uses a high speed processor to control the testing of digital printed circuit boards.
U.S. Pat. No. 4,108,358 issued to Casimer Niemaszyk also concerns a computer-controlled test apparatus for printed circuit cards and the like and employs the concept of a pin electronics package located near the device under test and remote from the controlling computer's main frame.